1. Field of the Invention
This invention relates to an improvement in a cooling system for an automotive internal combustion engine, and more particularly to a cooling system by which exhaust emission and fuel economy are improved.
2. Description of the Prior Art
Most automotive internal combustion engines, in general, employ a cooling system in which liquid engine coolant (cooling water) is forced to circulate through the engine by means of a coolant pump in order to cool the engine. The engine coolant after circulating the engine is introduced into a radiator which dissipates the heat which the coolant has absorbed from the engine. Additionally, a thermostat is provided in a coolant passage upstream of a radiator inlet to regulate the amount of the coolant flowing to the radiator in response to the temperature of the coolant, thereby controlling the coolant temperature at an optimum range. However, with such a cooling system, the cooling capacity due to the thermostat is set to be suitable for a high engine speed and load operating range, and therefore the thus controlled coolant temperature becomes unsuitable at a low load engine operating range or a no load engine operating range including idling. This inevitably deteriorates fuel economy and hydrocarbon exhaust emission.